A patent document 1 discloses a conventional gear shift control apparatus for a continuously variable transmission. In this conventional control apparatus, a, so-called, low return control is executed in which, in a case where a transmission gear ratio (a speed ratio or a shift ratio) is not a lowest gear ratio, the gear shift ratio is modified to a speed reduction side when a vehicle speed is zero so that the vehicle is in a stopped state. Thus, a favorable acceleration performance is exhibited during a re-acceleration of the vehicle after the vehicle is stopped.
However, the following problem is present in the above-described gear shift control apparatus for the continuously variable transmission. Such a vehicle is present that a, so-called, coast stop control function, viz., a supply of fuel to an engine is stopped in a low vehicle speed traveling state in which an accelerator pedal is released and a brake pedal is depressed.
When both of the coast stop control and the above-described low return control are used together, the engine is stopped before the vehicle is stopped due to the coast stop control. Thus, during the vehicle stop, the continuously variable transmission is in a state in which the gear shift ratio is kept at the gear shift ratio higher than the lowest gear shift ratio. If the low return control is executed in this state, there is often a case where the engine needs to be restarted in order to secure a hydraulic pressure required for the low return control. There is a possibility of an overload applied onto a clutch when the engine is started during the low return control.
It is necessary to make a line pressure high in the low return control. When the engine is started to actuate the clutch in a high line pressure, a clutch actual pressure (denoted by a solid line in FIG. 4) with respect to a command pressure (denoted by a broken line in FIG. 4) generates a hydraulic pressure surge shown in an eclipse broken line after a dead time td. Consequently, the overload is applied to a damper of the clutch.
With the above-described problem in mind, it is an object of the present invention to provide a control apparatus for a hybrid vehicle which can prevent an action of an overload applied to the clutch so as to deteriorate the clutch in a case where the coast stop control of the engine and the low return control are used together.